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Dec. 3, 19,46. v KESSLER Re 22,813

' TELEPHONE SYSTEM Original Filed Feb. 3, 1938 10 Sheets-Sheet 1 FIG. 1

WAY

i AuTo'MAnc EXCHANGE 'l o FINDER SWlTCH SWITCH FINDER ECT I SWITCH SWITCH I I OMATIC SWITCHING EQUIPME INVENTOR. FRANK KESSLER A'ITORNEY.

. 3, 1946. F. KESSLER TELEPHONE SYSTEM Original Filed Feb. 3, 1938 1o sheets-sheet 2 FIG. 2

mvsmon FRANK KESSLER ATTORNEY.

km x I is i fi oa a B J amma 1946- F. KESSLER R 2,813

TELEPHONE SYSTEM Original Filed Feb. 3. 1938 10 Sheets-Sheet v4 Y FRANK KESSLER ATTORNEY.

Dec. 3, 1946. F. KESSLER Re 22,

TELEPHONE SYSTEM 7.

Original Filed Feb. 3, 1938 10 Sheets-Sheet 5 H TIT II o o m I 0 C 3 (I) a: o h u LU Z z o u INVENTOR. FRANK KESSLER ATTORNEY.

F. KESSLER TELEPHONE SYSTEM Original Filed Feb. 3, 1958 '10 Sheets-Sheet 6 R L 5 5 E K A R F flw 5:3:

ATTORNEY.

Dec. 3, 1946, F. K/ESSLJER I Re 22,813 I TELEPHONE SYSTEM Original Filed Feb. 5, 1958 10 Sheets-Sheet 7 ING RELAY 1mm FRANK KESSLER ATTORNEY.

FIG. 7 v

Dec. 3, 1946.

F. KESSLER TELEPHONE SYSTEM 10 Sheets-Sheet 8 Original Filed Feb. 5, 1938 FRANK KESSLER Z44 ATTORNEY.

0 255%: N28 :5 fix F. K ESSLER TELEPHORE SYSTEM Original Filed Feb. 3, 1938 I 10 Sheets-Sheet 1O m n 5 5 m as 9 c 2 R 2 R m Ill 2 3 m w. new m m B I m MI m mww R on m m m 2 m m J 1 M H m .25 EH: m E2 62v 223 :25 Em ii M c J H 1 w H u I... I..." H PIA". T n F 1 9 Pl r M k a w n l I.

mvsm'on FRANK KESSLER ATTORNEY.

1 UNITED STATES ATsNr OFFICE TELEPHONE SISTEM Frank Kessler, Lombard, Ill., assignor to Automatlc Electric Laboratories, Inc., a corporation of Delaware Original No. 2,177,069, dated October 24, 1939, Se-

rial No. 188,443, February 3, 1938. Application for reissue January 25, 1943, Serial No. 413.545

38 Claims. 1 The present invention relates to telephone systems and more particularly to small automatic telephone systems of the type adapted for installation in small towns or villages.

An automatic telephone system of the character noted is generally known as a community automatic exchange or C. A. X and usually has a line capacity of one hundred lines or less. Forreasons of economy, the lines are usually of the multi-party type and code ringing is utilized for selectively signaling the telephone stations on.v

the various subscriber lines. In order to provide toll service to the subscribers, provisions are also made for trunking calls to and from one or more distant exchanges. One improved all-relay telephone exchange of this type is disclosed and claimed in the copending application Serial No.- 86,046 (Norman H. Saunders), filed June '19, 1936.

In" brief, in the system as disclosed in the above-mentioned Saunders application, the subscriber and trunk lines extend to the finder and connector switches of each of a plurality of allrelay finder-connector links, common equipment including a relay type link distributor or allotter being provided for assigning idle ones of the links to successive calling lines in a predetermined order. The finder switches of the various links are semi-directive in character; that is, it is necessarv to hunt for the calling line in a previously marked group of lines during the operation of a link to seize the calling line. Although this arrangement is entirely satisfactory from an operating standpoint, a substantial interval of time is consumed by the finder switch in hunting the calling line in the previously marked relay type which is fully directive in character. Another object 01' the invention is to. provide in a telephone system including a plurality of finder switches, improved allotter or distributor equipment associated with the finder switches for assigning in a predetermined order idle ones of the finder switches to the use of calling lines.

A further object of the invention is to provide allotter or distributor equipment associated with thefinder switches of a telephone system which is operable to assign an idle'one of the finder switches to the use of the next calling line immediately after a previously assigned one of the finder switches selects a calling line and to prevent the assignment ofthe previously assigned finder switch as long as the selected calling line is busy, and an improved arrangement responsive to a fault in one of the finder switches for causing operation at the allotter or distributor equipment to prevent the assignment of the one finder switch.

connected thereto. I

It is an object of the present invention to provide, in a'telephone system of the character noted, an improved line finder switch of the all-relay type which requires .a minimum numthe associated common equipment.

It is another obiect of the invention to provide, in a. telephone system of the character noted. an improved line finder switch of the all- Another object of the invention is to provide in a telephone system, a numerical switch ihaving access to a plurality of trunk and subscriber lines, and including improved apparatus selectively controlled in accordance with difierent' relations between the line selecting: digits for causing the operation of the numericaiswit'ch to provide trunk and subscriber line'selectiton.

A further object of the invention is to provide switch to select aypreviously selected idle one oi the trunk lines, and improved apparatus responsive to the selection of the one trunk line in immediately selecting another idle one or the trunk lines for use.

The features of the present inventionv are illustrated as being incorporated in a telephone exchange having an ultimate capacity or one himdred lines. The lines are arranged in a plurality of groups of. ten lines each of which is individually divided into two subgroups of five lines each, certain of the lines being twober of relays both in the switch itself and in way inter-office trunk lines, others of the lines being private exchange or P. B. X trunk lines, and the remainder ofthe' lines being subscriber lines. The various lines individually terminate in line circuits which are connected in the same manner regardless of whether a line'is a trunk or a subscriber line. The telephone exchange also includes a nluralitr or finder-connector links which individually have access to the lines,

omesortheor the subgroups. depending upon the operated or non -operated condition 0! the subgroup relay. More specifically, each group oi lines is divided into two subgroups respectively comprising odd and even numbered lines and the arrangement is that, when ascall is initiated on an odd line, the corresponding group and unit relays operate, without operating the subgroup relay, in the finder switch 01 the assigned link to select the 4 v switch or the assigned link to be operated. Also, the second auxiliary relay in the common equipment causes the operation or the control relay 0! the finder switch of the assigned link, which latter relay causes the previously conditioned group, unit and subgroup relays in the finder switch to select the calling line. This arrangement renders the finder switch fully directive and reduces the time required in extending a connection tom a calling line to an idle link.

For the purpose of assigning, in a predetermined order, idle ones of therfinder switches to the use of calling lines, there is provided, in association with the several links, allotter or distributor equipment including a' group of allotter relays individually corresponding to the links.

. In accordance with a further feature of the inodd calling line. On the other hand, when a call is initiated on an even line. the corresponding group and unit relays and the subgroup relay operate in the finder switch of the assigned link to select the even calling line. This arrangement reduces the number of unit relays required in each finder switch by approximately one-half and results in a considerable reduction in the manufacturing cost of the finder switches.

In accordance with a further feature or the invention, th group relay and the unit relay in a finder switch of an assigned link are arranged to operate substantially simultaneously to select vention, each of the allotter relays is provided with operating and holding circuits for energizing the same, and circuits controlled by the operation or the allotter relay also being provided ior assigning idle ones or the finder switches to the use or the lines having a calling condition thereon, and for preventing the assignment of the corresponding finder switch to the use of the lines having a calling condition thereon. More particularly, the arrangement is such that when a line in one of the subgroups; and the group relay, the unit relay and the subgroup relay in the finder switch of an assigned link are. arranged to operate substantially simultaneously to select a line in the other or the subgroups. This is accomplished by providing common equipment for controlling the operation of a control relay provided in each of the finder switches. More particularly, the common equipment comprises a group or first auxiliary relays individually corresponding to a particular group oilines and to a particular group relay in. each finder switch, a group of second auxiliary relays individually corresponding to a particular line in each subgroup of lines and to a particular unit relay in each finder switch, and a third auxiliary relay corresponding to one of the subgroups in each group of lines and to the subgroup relay in each finder switch. With this arrangement and when a call is initiated on a particular line in one 0! the subgroups, the corresponding first and second auxiliary relays in the common equipment are operated and cause the corresponding group and unit relays in the finder switch oi! the assigned link to be conditioned, to be operated. Also, the second auxiliary relay in the common equip- Y ment causes the operation of the control relay provided in the finder switch or the assigned link, which latter relay causes the previously conditioned group and unit relays in the finder switch 01' the assigned link to operate substan-.

tially simultaneously, thereby to select the calling line. When a call is initiated on a line in the other of the subgroups, the corresponding first and second auxiliary relays and the third.

auxiliary relay in the common equipment are operated. Thefirst and second auxiliary relays in. the common equipment condition the corresponding group and unit relays in th finder switch of the assigned link to be operated, and

the third auxiliary relay in the common equipment conditions the subgroup relay in the finder completed. Upon operating, the allotter relay completes its holding circuit, assigns an idle one of the finder switches to the use of the next line having a calling. condition thereon, and prevents the assignment or the corresponding finder switch to the use 01' lines having a calling condition thereon. Idle ones of the finder switches are operated successively until the last finder switch in the group is taken for use by a calling line. At this time the holding circuits of all of the allotter relays are interrupted and those allotter relays corresponding to' idle finder switches restore to recycle the idle finder switches for use 'by the lines having a calling condition thereon.

In accordance with a still further feature of the invention, an arrangement is provided in association with each of the allotter relays for operating the same in response to the presence of a fault in the corresponding finder switch, in order to prevent the assignment or the corresponding finder switch td-ithe' uses! one of the lines having a calling condition thereon. More specifically, each of the allotter relays is provided with an additional operating circuit for energizing the same, which is controlled by a fault detector comprising a fuse link individual to the corresponding finder switch. When a fault appears in one of the finder switches, the fuse link individual thereto is operated or blown, causing the additional operating circuit of the corresponding allotter relay to be completed. Upon operating, the corresponding allotter relay prevents the assignment of the finder switch having a fault therein to the use of one of the lines hav-.- ing a calling condition thereon. I

In accordance with another feature of the invention, each numerical or connector switch 01' each link isprovided with apparatus, including a group of impulse counting relays for causing operation of the numerical switch to provide trunk and subscriber line selection in an improved manner. More particularly, the apparatus is responsive to a predetermined digit and a predetermined digit following the first-mentioned digit for causing the operation or the .I8. Also extending to earns switch to select a particular subscriber line, and is responsive to the first-mentioned digit and a dliL-rent predetermined digit following the firstmentioned digit for causing the operation or the switch to select an idle one'ot a certain group 01 trunk'lines.

In accordance with a still further object of the invention, an improved arrangement is provided in conjunction with the last-mentioned group of trunk lines for assigning idle ones of the trunk lines to be selected by the numerical switches in a predetermined order. This atrangement is such that an idle one of the trunk linesis assigned tor-the use of the numerical switches immediately following the seizure of a previously selected one oi the trunk lines by one of the numerical switches.

Further features of the invention pertain to a' particular arrangement oi the circuit elements whereby the above-outlined and additional operating features are attained. a

The novel features believed to be characteristic 6 I connector switch 888 which two switches are connected together by link Hues to form" a finderconnector link. Similarly, the line 88 terminates at a line circuit 88'; and the illustrated two-way trunk lines 2I and II interconnectingthe exchange I8 and the exchanges tit and I88, respectively, terminate at line circuits 2| and 8|, re-

Bpectively.

As many as ten telephone stations may be connected to each multi-party subscriber line, these telephone stations being arranged in two groups of the invention are set forth in theappended claims. The invention, both as to its organization and method of operation, together with further objects andadvantages thereof, will best be understood by reierenceto the specification, taken.

in connection with the accompanying drawings, in which Figure 12 illustrates the general arrangement 0! a system embodying one form of the present invention; Fig. 9 illustrates the mode of combining the remaining figures of the drawlugs to form a unified system; and Figs. 1 to 8, inclusive, 10 and 11, illustrate the details of a system having incorporated therein the features of the invention as briefly outlined above.

Referring now more particularly to Fig. 12 oi the drawings the telephone system there illusis indicated at 2| as terminating at a. repeater I81;

and one of the second group of inter-ofllce trunk lines is indicated at 8i as terminating at a repeater I88, the repeaters I81 and I88 forming Parts of the apparatus located at the exchange the exchange I8 are two groups of private branch exchange or P. B. X trunk lines, not shown, which are accessible to the finder and connector switches 01' the links included in the exchange I 8. Also extending to the exchange I8 are a plurality of subscriber lines, two of which are indicated at 28 and 88. Each of the enumerated subscriber lines is illustrated as being of the'multi-party type having two or more telephone stations associated therewith. Thus, two telephone stations, IB and 2B are diagrammatically shown as being connected to the line 28, and two additional stations, ID and 2D, are diagrammatically shown as being connected to the line 88. Each of the substations connected to the various subscriber lines may comprise the usual hand set having embodied therein a conventional dial-controlled impulsing device. Each 01' the lines extending to the exchange I8 termihates ina line circuit through which it is rendered accessible to the finder and connector switches of the links included in the exchange. Thus, the

line 28 terminates at a line circuit 28', through which it is connected to the contact springs or a finder switch 288 and to the contact springs of the is assigned by I comprising five telephone stations each. The sig-' nals or ringers or one of the groups of telephone stations are connected between'one side 01' the subscriber line and ground, while the ringers of the other group of telephone stations are connected between the other side of the subscriber line and ground, thereby providing an arrangement utilizing divided ringing.

As indicated above, the exchange .I 8 is designed to serve a relatively small number oi lines comprising two groups of inter-oillce trunk lines, two groups of P. B. X trunk lines, and a plurality of subscriber lines, these lines being arranged in ten groups of ten lines each. Accordingly, all of the trunk and subscriber lines are arranged to be served by any one of a plurality oifinder-connectorlinks included in the exchange ously, the number of links required for satisfactory service will depend upon the volume of telephone trafllc, but, taking into account the char- I acter of the exchange, ten links are considered adequate for reasonably good service. In order to assign the links to successive calling lines in a predetermined order, so that a link is always available for the use of a. calling line, excepting, of course, those instances when all of the links are simultaneously busy, there is provided in association therewith common equipment indicated at 88! which includes a link distributor or allotter. The several links also have associated therewith common, ringing tone and timing apparatus which is diagrammatically shown at88fil. I

The operation 01' the system to extend a call I initiated atgany one of the telephone stations to another, of the telephone stations is described briefly below, neglecting the details of the circuit arrangement. In extending a call initiated at one of the telephone stations to one of the telephone stations connected to a subscriber line included in the second, third, fourth, fifth, sixth or seventh group or ten lines, a corresponding tens "digit, a corresponding units digit and a corresponding coderinging digit are dialed, in the order named, at the telephone station when the call is initiated. For example, when a subscriber at the telephone station IB connected to the line 28 initiates a .call, by lifting his receiver from its switch hook, which is to be extended to the telephone station ID connected to the subscriber line 88, or the tenth line in the third group of ten lines, the line circuit 28' operates to cause the finderconnector link previouslyassigned by the link distributor orallotter in the common equipment "I to the calling line, to be set into operation to seize the calling line. Assuming that the link 888 the link distributor to set up the connection, the finder switch 288 of the link operates to select the calling line ahd to connect it through to the conductors of the link line incoming to'the connector switch 588 of the link. When the calling line 28 is seized and extended by way of the finder switch 288 to the associated switch 888, it is marked as busy in all of the other connector switches of the links, and the control I. 1 Obvi-- phone station is being signaled.

' ratus is such that a link utilized in setting up a equipment of the soiled link is automaticallyconditioned to respond to the impulses of the first digit transmitted from the impulsing device provided at the calling telephone station IB. Since the subscriber lines are of the multi-party type, provisions are made for selectively signaling the desired 'calledtelephone' station onany selected subscriber line. With the arrangement to be described more in detail hereafter, coded ringing is utilized to accomplish this end. 1 The connector switch I" of the link lli'fi sponds to the impulses of the tens digit 3 at the calling telephone station by selecting the third group of ten lines which includes the called line Ill. Thereafter, and in response to the dialing of the units digit 0, the called line a .is selected from the selected group of ten lines.

' When the called line is selected, the control apparatus included in the link circuit functions to test this line for the purpose of determining the busy or idle condition thereof. If the called line is busy, busy tone current is applied to the link line and returned over the loop to the calling telephone station to indicate to the party at the calling telephone station that the desired connection cannot immediately be completed.

On the other hand, if the called line is idle at the time it is selected, the code selecting or ringlng digit which is dialed at the calling telephone station, causes a selected coded ringing current to be appliedto the side of the line to which the ringer of the telephone station ID is connected, the code of the selected ringing current corresponding to the called telephone station ID. While each of the ringers of the telephone stations included in the group of telephonestations with the telephone station ID are operated, the character of the code 'ring indicates that the telephone station ID is the telephone station being called. During the ringing operation, ringback tone current is applied to the loop extending to the calling telephone station to indicate to the party at this station that the desired called tele- Finally, a connection between the calling and called telephone stations is completed when the call is answered at the called telephone station iD. As pointed out with particularity hereinafter, the arrangement of the link circuit appadesired connection is released only when the connection is-cleared out at the calling telephone station.

In extending a' call initiated at one of the tele phone stations to one of the telephone stations connected to a subscriber line included in the first, eighth, ninth or tenth'group of ten lines, a predetermined prefix digit, 9. corresponding tens digit, 9. corresponding units digit, and a corresponding code ringing digit are-dialed. in the oran der named, at the telephone station initiating the call. For example, when a subscriber at the tele phone station [3 initiates a call, by lifting his receiver from its switch book, which is to be extended to a telephone station connected to a particular subscriber line included in the first group of, ten .lines, the "line circuit Ill operates and causes the finder switch of a previously assigned finder-connector link to be operated to seize the calling line, as previously explained. When the predetermined prefix digit is dialed at the callin telephone station 1B, the seized link is conditioned to operate its connector switch to select the first, eighth, ninth or tenth groups of ten lines. Thereafter the connector switch responds station by selecting the firstgroup dialing oi. the units digit, corresponding tothetensdigitldlaledatthecalling oftcnlinel. Thereafter the connectorswitch responds particular subscriber line to which the telephone station is connected. to select the called subscriber line irom the selected group of ten lines. The operation or the system to test the selected line for the purpose oi determining the o busy'or idle condition thereof and to apply busy tone current to the link line-in the event that the selected line is busy is the same as that previously described. Also, the system operates, as described above, to cause a selected coded ringing current. corresponding to the called telephone station, to be applied to the side of the line to which the ringer of the called telephone statim is connected u on dialing the code selecting digit at the calling telephone station IIB. A connection between the calling telephone station IB andthe called telephone station connected to the particular line in the first group of ten lines is completed when the call is answered at the called telephone station. The switching apparatus located in the exchange l0 may also be utilized in setting up a connection between two telephone stations con-' nected to the same subscriber line, the sole function of the apparatus in this regard being that of selecting and applying ringing current to the calling line of the proper code to signal a party at the called telephone station. Carrying out this function necessitates the seizure of the calling line by an idle link, in the manner described above. Thereafter, and following the dialing of the digits of the directory number of the called telephone station at the calling telephone station,

the calling part-y replaces his receiver upon its switch hook. When the calling party hangs up, the finder switch of the operated link is released and ringing current of the selected code corresponding to the called telephone station is applied to the calling line. When the call is answered, the operated link is released and the line circuit of the line in service is operated to busy the line, thereby to prevent seizure of the line by the connector switch of another link when another telephone station initiates a call to be extended to one of the telephone'stations on the line. hangs up he removes the receiver from its switch hook to converse with the party at the called telephone station. Finally, the line circuit of the line in use is released when the connection is cleared out at the calling and called telephone stations.

As heretofore pointed out, the inter-ofllce trunk lines are arranged in two groups. More specifically, the first group is included in the second group of ten lines, and the second group is in- I cluded in the third group of ten lines. .In the operation of the link to select one of the first group of inter-ofilce trunk lines including the line 2| interconnecting the exchange 'lb and the exchange ili only one predetermined digit "X comprising a predetermined number of impulses is dialed at the calling telephone station. The

' connector switch of the seized link responds to the impulses of this one digit to select a pre- I viously assigned idle one of the first group of trunk lines. More specifically, these inter-omce trunk lines have, associated therewith apparatus for setting up idle ones of thelines for selection by the connector switches. which apparatus functionstoassignanidlelineforuseimmediately A reasonable time after the calling party Hence, at .the conclusion or the predetermined trunk selecting digit dialed at a calling telephone station, the connector switch oi the seized linkimmediately operates to select the previously assigned idle trunk line. selected, the calling line is switched through by way of the selected trunk line and its associated repeater circuit to the terminating apparatus located in the exchange I85. In this connection, it is pointed out that two sets 01 link line con-. ductors are provided in the link circuit of; each link, one set 01' which is devoid of all voice fre- Whenthe trunk line is.

I after a previously assigned line is taken for use.

quency coupling. elements such, for example, as

condensers or repeating coils, and is utilized in extending a connection by way of one of the trunk lines. Following the extension of the connection to the trunk line terminating apparatus located in the exchange I85, the connection may further beextended to a desired called telephone station such, for example, as the telephone station A, by dialing the regular directory number corresponding to the line to which the telephone station A is connected. The manner in which the connection is released following the establishment of a connection to the telephone station A depends upon the nature oi the repeater circuit associated with the-trunk line which is used in setting up the connection.

Since the trunk linesinterconnecting the exchanges it! and I85 are of thetwo-way type, it

. will be understood that any one of these lines of the switching apparatus included in the exchange l0 may be utilized in the completion of calls originating or extended by way 01' the exchange I85, and which are to be extended to one 01' the subscriber lines terminating at the exchange Ill. The mode of operation of the equipment in the exchange in following the extension of a call H thereto by way of one or the lines in the first group oi. trunk lines is substantially similar, to

that set forth with reference to the connection established between the telephone stations IB and ID,

In the operation 01' the link to select one 01' the second group of inter-omce trunk lines including 'the line 3! interconnecting the exchange iii and the exchange I86, only onedifierent predetermined digit "X comprising a predetermined different number of impulses is dialed at the calling telephone station. The operation and arrangement of this'apparatus for selecting an idle one of the trunk lines in the secondgroup of inter-office trunk lines are otherwise the same as that of the apparatus for selecting an idle one of the trunk lines in the first group of inter-oflice trunk lines, asdescribed above.

As heretofore pointed out, the P. B. X trunk lines are arranged in two groups. The first group is included in the ninth group of ten lines, and the second group is included in the tenth group of ten lines. To select an idle one of the first group of P. B, X trunk lines, the number ,P, X, Y, R is dialed at the calling telephone station, the digits P, X and Y being diiferent in character and the digit R beingany desired ringing digit. More specifically, the number 8911 is dialed at the calling telephone station. When the prefix digit 8 is dialed, the seized link is .conditioned to operate its connector switch to select the first, eighth, ninth or tenth group of ten lines. Thereafter the connector switch responds to the tens digit 9 to select the ninth group of ten lines. Thereafter the connector switch responds to the units digit 1 to select a previously above.

fifl i nedidleoneoithe'firstgroupoiRnx trunk'lines. More specifically, the first group of P. B. X trunk lines have associated therewith apparatus iorsetting upidle ones of the lines to be selected, which functions to assign an idle trunk line for use immediately after a previously assigned trunk line is taken ior use. Dialing of the ringing digit 1 causes coded ringing current corresponding to the code ringing digit 1 tube appliedto the selected P. B. x trunk line in order to signal the operator at the privatebranch exchange connected thereto. A connection between thecalling telephone station and the operator's station at the private branch exchange is completed when the call is answered at the operator's station.

. As' indicated above. onlya portion of the lines I or the ninth group are P. B. X trunk lines, the remaining lines of this group being subscriber lines." The connector switch arrangement is such that. when the digits 1?, X, an'd'X or Z are dialed into one of the connector switches one of the sub scribers lines of the ninth line group is selected. For example, if the. number 899 or the number 896 is dialed at a calling telephone station the connector switch of theassigned link responds by selecting the particular subscriber line of the ninth line group corresponding to the units digit 9or6. a

In order to select an idle one of the second group of P. B. X trunk lines the number 8011 is v ,dialed at the calling telephone station. The operatlon and arrangement of this apparatus .for selecting an idle one of the second group of P. B. x trunk lines are otherwise the same as that oi the apparatus for selecting an idle one of the first group of RB. X trunk lines described Considering now in greater detail the,apparatus embodied in the exchange I! andinvolved in the above-described sequence of operations, and

reierringto-Flgs. 1 to 8, inclusive, 10 and 11 'of the drawings, there are illustrated the elements of the line circuits 2|, 20', 3|, and 38' terminating the lines 2|, 20, II and 30, respectively, the elements of the finder-connector link ill, and the elements of the distributor and common equipment 69L There are alsodiagramm'atically il-v lustrated those portions of the ringing. tone and timing apparatus Bill! which are essential to an understanding oi theoperation of the system. The line 'clrcuits individually terminating 'the subscriber and trunk lines are of more or less conventional arrangement More particularly, the line circuit 20 terminatingthe subscriber line 20, comprises a line relay Rlzfia cutoil relay RH,- and a line lock-out relay RI i5 connected and arranged to operate in the usual manner. The corresponding relays of the line circuit 30' terminating the subscriber line 30 are indicated at Rl55, RIBD, and RI, respectively,

"The line. circuits individually terminating the respective trunk lines are identical in character and circuit arrangement. More particularly, the line circuit 2 i terminating the inter-oflice trunk line 2! comprises a line relay RI ii, a cut-oi! relay Rlili, and a line lock-out relay RIM. flhe corresponding relays oi the line circuit 3| terminating the inter-ofiice trunk line it" are'indicated atRlll, RI and Rllil.

Each of the finder switches is of the fully directive all relay type, group and unit relays being provided for performing the line selecting functions. The lines terminating at each finder" switch are arranged in'groups of and i the lines of each group springs of one group or gang relay. More paring thetwo relays R210 and R200 individually having contact springs for terminating the con- '9, 1936. The lines of each group are divided into twoequai subgroups respectively comprising the odd numbered lines and the even numbered lines, and, through the provision or a. subgroup relay in each finder switch, a group of five unit 1 relays is suiiicient to permit the selection oi any desired one of a selected group of ten lines. Thus, the finder switch 200 comprises a subgroup relay R225, and fiveunitrelays R200, R205, R! l0, R218 and R220, each of which unit relays is operative to select either 01' two lines in a' selected group of ten lines depending upon the operated or nonoperated condition of the subgroup relay R225.

The finder switch 200 also includes a pair 01' switching or control relays R230 and R240 which are arranged to be. controlled by way of the common equipment I illustrated in Fig. 6, and are operative to initiate the operation of the finder switch to seize a calling line.

terminate at the contact" t-icularly, the finder switch 200 comprises ten group or gang relays correspondlngto and includ- -ductors of ten lines. While the group relays may 12 am is energized and operates to condition the subgroup relay embodied in the finder switch oi! the selected link for operation. In order to give the finder switch of any assigned link ample time to seize the calling line to which, it is assigned and to connect the'line through to the connector switch or the link before the common equipment "I is reconditioned to respond to another call,

a relay R880 is provided, which relay is operative immediately a link starts to seize a calling line V -The link allotter or distributor 800 isiliuslink seizes a calling line and to prevent the assignment of the corresponding link to the use of a calling line. The allotter relays are operated successively to assign the links to the use The common equipment 89! shown in Fig. 6

includes a plurality of first auxiliary relays which are arranged to be-energized over start circuits controlled by theline circuits associated with the respective lines terminating at the exchange 10.

' finder switch or an assigned link. More particularly, ten first auxiliary relays including the three relays R800, R8l0 and R820 are provided, which individually correspond to the gang relays ,em-

' bodied in the finder switch of each link. A group oi' five second auxiliary relays R835, R840, R808,

R880 and R885 are similarly provided which individually correspond to the unit relays embodied in the finder switch of each link and are operative to condition the corresponding unit relays eration. The energization of the subgroup relay in the finder switch of an assigned link is in the finder switch of an assigned link for opdependent upon the operated ornon-operated condition of a third auxiliary relay R880 provided in the common equipment, this latte relay also being arranged to be energized over those oi. the start circuits which are adapted to be completed in the line circuits terminating the lines included in predetermined ones of the line subgroups. Speciflcaily, the arrangement of the apparatus is such that when a calling condition is created on one of the lines terminating at the exchange, start circuits are completed by the line relay associated with the calling line for causing the operation oi the one of the first auxiliary relays R800, R8l0, etc., which corresponds to the group of lines including the calling line and for energizing the one of the second auxiliary relays R835, R840, etc., which is operative to select the particular calling line. It the calling line is in one subgroup of its particular group the third auxiliary relay R830 is not energized over the completed start circuits, but it the calling line is in theother subgroup the third auxiliary relay or calling. lines; and after the tenth allotter relay oithe group operates, the control relays R088 and R810 are operated to recycle the allotter relays in order to provide for the reasis provided. in the exchange for the purpose of signaling a supervisory operator in one of the distant exchanges in the event a fault appears in any one of the links. The alarm apparatus 880 comprises a start relay R800 operative in response to an urgent fault in the link, a start relay R000 operative in response to a non-urgent fault in the link, a local alarm or buzzer 88L and a plurality of control relays R083, R088, R810 and R815. Each 01' the fault detectors comprises a device operative'in response to the presence oi a fault in the finder switch oithe link, a deviceoperative in response to the failure of the ring pick-up relay to operate in order to apply ringing current to a selected line, a device operative in response to the presence of a hot coil in certain of the relays associated with the link, and a device operative in response to an undercharged condition of certain of the batteries associated with the link The first two devices mentioned above operate to cause the operation of the start relay R800, while the lust two devices mentioned switch having a fault therein, thereby to prevent the allotter 800 from assigning the finder switch to the use of calling lines, in addition to causing operation of the start relay R880. Each of the start relays R880 and R080 is operative to initiate the operation of the alarm apparatus 880 I to cause the operation 01' the above enumerated control relays, thereby to actuate the buzzer 0", to actuate an alarm in an alarm center line.

. 13 and to condition the ringing apparatus Ill to apply a characteristic tone current to the line ilii tor the purpose oi informing a supervisory operator as to the nature of the fault.

The link circuit proper is illustrated in Figs. 3, 4, 7 and 8 o! the drawings. The link line conductors Clitl and Ci!" are arranged to be included in the operating circuit of the line relay R3). The line relay Rl0 is of the usual impulse responsive type and in combination with the two additional relays R300 and RSI! forms an impulse correcting network for repeating impulses transmitted thereto from a calling telephone station over an impulsing circuit to the slow-to-release control relay R800 and the impulse counting relays illustrated in Figs. 8 and 7, respectively. The link hold relay is indicated at R32. The relay R300 is the usual switching through relay which is energized only when the link is utilized in extending a connection by way of one oi the inter-oii'ice trunk lines to one oi the distant exchanges I00 or I88. The called party pagers answer relay is indicated at R000, thi relay being I arranged to operate in the usual manner when a call is answered at or called substation, and functions to control the operation of a slave relay R030 which performs the battery reversing operation. For the purpose of preventing the link from being permanently tied up through seizure by a defective line or a line having a, calling condition present thereon for an unreasonable time interval, there is provided a link release relay R3 and .timing apparatus diagrammatically illustrated at 310. This timing appa ratlls may be of any desired construction which includes means for applying ground pulses to the conductor Cifll at spaced intervals, which normally retains ground on the conductor Cifli, and which removed ground potential from the conductor (H212 at intervals spaced from the intervals during which ground potential is applied to CH2". If desired, this apparatus may comprise a commutator driven by a synchronous motor through a gear reduction box and including commutator segments suitably arranged to control the application or ground potential to,

the two leads (H212 and Clfll in the manner described.

The counting relay networkv illustrated in Figs. '7 and 8 includes ten impulse counting relays R100 to EH90, inclusive, which relays are soquentially operative in response to the impulses of each oi a plurality of series of impulses transmitted to the connector switch 000 and function to control the selection of adesired called line and to control the selection oithe'code' of the ringing current to be projected over the called Each ofthe counting relays'is arranged to be locked energized in series with a corre-. sponding one oi the three'control' relays R8l0, R820 and R030 and to be deenergized in response to the operation of its succeeding counting relay in the manner described in detail hereinafter.

14* of short and long pulsating battery impulses.

The switching irelay R410 functions to connectv the link line conductors Gilli and Cl 303, incoming to the link circuit, by way of voice frequency coupling apparatus to the linkline conductors Cilli and 01200, outgoing from the link circuit, to cause operation of a'riug pick-up relay R430 and to initiate the operation of the code interrupter apparatus I000. The switching relay R4i0 is controlled by the control relays R8l0, R820 and R830, which latter relays are controlled by the countin relays R100, RIIO, etc., in their response to the'impulses of a code. selecting digit dialed at a calling telephone station. The counting relays also select one of the interrupter leads to apply coded ringing current to one side of the selected line, and control the operation of a generator reversing relay R440 which functions to select the side of the selected line to which the coded ringing current is to be applied. In order to terminate the ringing oper- "ation when a call is answered at 9. called telephone station there is provided a ring cut-oi! relay R450 whichis operative to terminate a The reverting c'all relay R400 cooperates with certain of the other relays to hold the connector switch 500 of the link 000 operated during the period when ringing currentis being applied to a calling line on a reverting call. Aiso, 'the' reverting call relay R400 operates when a predetermined prefix digit is dialed at a calling telephone station to control the operation of the prefix digit relay R340, which latter relay controls the prefix digit slave relay R400. These latter two relays function to condition the connector switch 500-to select a line in the first.

eighth, ninth or tenth groups of ten lines, as previously explained. The busy relay R420 is provided for the purpose of causing busy tone current derived from the busy and dial tone apparatus 040 to be applied to a calling subscriber line when a selected called line is found busy.

In order to rearrange the circuit connections so that the counting relays are rendered effective to perform difierent duties during the successive series of impulses transmitted thereto, two transfer relays-R410 and R400 are provided, in addition to the prefix digit relay R340 and the prefix digit slave relay R400. More particularly, the

relays R340and R460 are arranged to operate v ones of the group" relays in the connector switch The ringing tone and timing equipment diagrammatically illustrated at 000 comprises ringing apparatus 850 and a code interrupter i000.

This apparatus is arranged in a conventional manner, the ringing apparatus 080 including a ringing generator fromv which ringin current is derived, and the code interrupter apparatus I000 being connected alternately to impress pulsating battery potential and groundpotential on each of the live interrupter leads GU34 to Cilll, inclusive, for coded intervals which are diflerent ior each of the leads and comprise combinations H selected, is illustrated in Figs. 5 and -11. y connector switch per se is similar to the finder of the link may be selected for enei gization; the

relay R410 is arranged to operate at the end of the second series of impulses corresponding to a tens digit to condition the counting relays to select one of the unit relays in the. connector switch of the link for energization and to condition the rent to be applied'to the selected called subscriber line.

The connector switch 500 of the link 300, including the apparatus for preassignin idle ones of the interomce and P. B. X trunk lines to be switch in that ten group or gang relays each ter- Thegin"

minating the conductors oi tenlines. live unit relays. and a subgroup relay are provided for performing the line selecting functions. Specifically, the connector'switch illustrated comprises ten 'gang relays correspondingto and including the two relays R010 and Run illustrated, nve unit relays R520, R030, am, am and am, and a subgroup relay R000. Here again, the-lines terminating at the contact springs of each group relay are divided into two subgroups and each unit relay is operative to select either of two 'lines', individually included in diflferent subgroups, depending upon the operated or nonoperated condition of the subgroup relay R000. Preferably, each oi the group relays R010, R500.

' etc., like each of the group relays oi the finder switch 200, is of the form. disclosed and claimed inthe copending application, Serial No. 109,813,

Herbert F. Obergfell, filed November 9, 1936.

The apparatus for preassigning idle ones of the inter-oillce trunk lines in the second group oi ften lines is common to all oi the links and in-' cludes a group of trunk select relays RI I00, RI I I and RII20, which individually correspond to the first, second and third inter-oillce' trunk lines terminating at the contact springs oi the second group relay R010, and a group of control V relays RII00, RI I02 and RI I04, which individually correspond to the inter-oilice trunks numbered from one to three in the second group ol' ten lines. As pointed out in greater detail hereinaiter, the two .groups of relays cooperate in a manner such that an idle inter-oflgce trunk line in the second ten line group is preselected and ready for the use oi' any one of the links so long as any of the trunk lines in this group is idle,and when allof the trunk lines become busy the link circuit apparatus of alink attempting to select one of the lines returns busy tone over the loo extending to the calling subscriber.

Thearrangement and operation of the appathe automatic exchange I00 and from thelatter I to the-selector switch I03 therein. Upon dialing the proper digit at the telephone station A. the call is extended from the selector switch I03 through the two-way repeater m to the odd numbered inter-oilice trunk line 2|, whereupon the line relay RIIO individual to theline 2| is CI200 of the line 2I, the repeater I01, the sefinder switch I02, the selector switch I03, the

'lector switch I83, the finders-witch I02, the telephone instrument at the telephone station A. the

repeater I01, the conductor CI20I o! the line 2i, RAI01 and the lower winding of Bill to battery. Assuming that the link illustrated is the link assigned by the allotte'r to the use of sistor 003 to battery. Thelinerelay RIII also completes at RAI I3 an operating circuit for the auxiliary unit relay R035, this circuit extendin from ground at RA03I by way'oi CI2I0, RAI I3. RAIN, CI2II, RA005, Cl-208, the winding of relay RA003, RA030 and the resistor 000 to battery.

Upon operating, the relay R000 completes at RA000 an obvious holding circuit for itself and prepares at RA000 a circuit for operating the gang relay R210 in the finder switch 200. Upon ratusfor preassigning idle ones oi. the ;interoihce trunk lines in the thirdgroup often lines trunk lines in the tenth group of ten lines are similar .to that of the apparatus for preassigning idle inter-oflice trunk lines described above. This apparatus comprises a group oi trunk selecting relays Rll50, RH" and Rlll' and a group of control relays RII00 and RII00 corresponding to the relays RIIIO and RI I00. apparatus (not shown) substantially the same I as that described for pre idle ones of the P. B.'X trunk lines in the tenth group of ten lines is provided for preassigning idle ones of the P. B. X trunk lines'in ten lines.

o eration of the finder switch totem a call initiated at a telephone station connected to an odd-numbered lineto a1: idle link 1 A call is initiated at a tel ephone'station connected to an odd numbered line by removing the receiver of the telephone instrument from its associated switch hook, thereby completing a circuit between the telephone station and the line relay individual to the odd numbered line.

the ninth group 01' batte y.

operating, the relay R030 completes at RA030 an obvious holding circuit for itself; completes at RA031 a circuit for energizing the control relays R230 and-R240 in parallel, and prepares at RA030 a circuit for energizing the unit relay R200 in the finder switch 200. The operating circuit of the control relays R230 andR240 extends from ground at RA001 by way of CI201, RA202, CI240'. and the windings 01' R230 and R200 in parallel to 1 Upon operating, the relay R200 completes at RA202 the operating circuit of the gang relay R210 and completes at RA240 the operating circuit oi the unit relay R200, the operating circult of the gang relay R210 extending from ground at RA000 by way of CI230, RA202, CI22I and the winding of R210 to battery, and the operating circuit oi the unit relay R200 extending from ground at RA030 by way of (H230, RA200, CI200 and the winding of R200 to battery. The relay R240 also completes at RA20I a circuit for energizing the relay R000, this circuit ex-- tending from ground at R000 by way of the winding of R000, CI205, RA20I, CI200, the link conductor CI203 of the link 300, RM, M030 and the upper winding 01' the line relay R3I0 to battery. Upon operating, the relay R000 inter rupts at RA002 a. point in the operating circuits of the auxiliary group relays R000, ROI0, etc., and interrupts at RAO0I a point'in the operating circuits of the auxiliary unit relaysR030, R000,

etc, thereby busying the allotter 000 so that it is non-responsive to other calls.

The gang relayR210 operates to close its contact springs connected to the lines numbered from 20 to 20 and the unit relay R200 operates to connect the calling line 2| to the link circuit oi the assigned link 300. When the line I R|05, circuit for energizing these relays extending from of R200 to battery.

relay R210, the conductor C|200 of the line 2|, the repeater I81, the selector switch I88, the finder switch I82, the telephone instrument at the telephone station A, the finder switch I82, the selector switch I88, the repeater I81, the conductor C|20| of the line 2|, the contact springs of the gang relay R210, RA208, Cl255,

. RA221, the link conductor C| 288, RA885, RAI85 and the upper winding 'of R8I0 to battery.

Upon operating, "the line relay R8I0 completes at RAIII a circuit for operating the link impulsing relay R805, this circuit extending from ground at RA828 by way of RA8||, and the winding of R808 to battery; interrupts at RA8I2 a point in the circuit extending from battery by way of the upper winding of R8I0, RA885, the resistor H and RA8I2 to the link control conductor CH8; and prepares at RA3I2 a point in ,theclrcuit for applying ground to the control conductor (H288.

Upon operating. the link impulsing relay R808 completes at RA809 an obvious circuit for operating the hold relay R820, which is of the slowto-release type, and an obvious circuit for applying ground to the control conductor CI288, thereby to mark the link 800 as busy in the allotter. When the control conductor CI284 is grounded, the lookout relay RI00 and the cut-oil relay individual to the line 2|, are operated, the

the grounded control conductorCIZBl by way of RA228. C|25 RA2M, the contact springs of the gang relay R210, the control conductor Cl202 of the line 2|, the winding of R|05 and the winding of RI 00 to battery. Upon operating, the cut-of! relay R|05 interru ts at RAIBG and RAI01 the operat ng circuit of the line relay RI I8. The line relay RI I0 then restores and interrupts at RAI I? the holding c rcuit of the relay R800 and interrupts at RAII3 the holding circuit of'the relay R885, and the latter relays restore. The lockout relay RI00 operates and interrupts at RA|02 a further point in the holding circuit of the relay R800 and interru ts at RA|03 a further point in the holding c rcuit of the relay R835. The presence' of ground potential on the control conductor CI 202 of the calling line serves to busy this line in the other automatic switches having access thereto. 7

Upon operating, the hold relay R320 completes at RA822 a holding circuit for itself, this circuit 8 extending from ground at RA322 by way of RA3|6 and the winding of R820 to battery; applies at RA823 multi'ple ground to the control conductor C|284 in order to retain the cut-oil relay R|05 and the lock-out relay R|00 individual to the line 2| operated during im ulslng periods; and completes at RA32| holding circuits for the operated gang relay R210 and the operated finder unit relay R200. The holding circuit of the opera ed gang relay R210 extends from ground at RA304 by way of RA82I, CI25I, the contact springs of R210 and the winding of R210 to battery, while the holding circuit of the operated unit relay R200 extends from ground at RAIN by way of RA82I, C|28|, RA|

The hold relay R820 also completes at RA828 a circuit for operating the start relay of the dial and busy tone apparatus 840, this circuit extending from ground at RA828 by way or C|802, RAlI8','the start lead CH8 and the winding 01' the start relay, not shown, in the dial and busy tone apparatus 840' to battery. The dial and busy tone apparatus 840 then operates to apply dial tone to the link 800, this circuit extendinl from pulsating battery in the dial and busy tone apparatus 840 by way of the dial tone conductor CI848, RM", RA482, RAIN, RAIN, the link conductor C|20 I, the condenser CI 29 I and RA"! to the link conductor (H288, through the te1ephone instrument at the telephone station A connected to the link conductors C|288 and C|28| by way oi'the finder switch 200,-the line 2|, the repeater I81, the selector switch I88 and the finder witch I82, and from the link conductor C|28I by way 01 RA882, the link conductor CI 282 and RA4|2 to ground. The party initiating the call at the telephone station A then receives dial tone indicating that a link has been seized and that he may operate the dialing mechanism associated with the telephone instrument to extend v the call from the link to the called line.

R8 I 0 and one of the relays Inca similar manner, when calls are initiated at telephone stations connected to the odd-numbered lines 28, 28, 21 and 29, respectively, the relay R800 and one of the relays R840, R848, R880 and R888, respectively, are operated in the auxiliary or common equipment. The relay R800 operates the gang relay R210, and the relays R840, R888, R880 and R855 operate the unit relays R205, R2| 0, R2|5 and R220, respectively, in the finder switch 200 to connect the lines 28, 28, 21 and 29, respectively, to the link Similarly. when calls are initiated at telephone stations connected to the odd-numbered lines 3i, 38, 88, 81 and 39, respectively, the relay R835, R840, R845, R855 and R855, respectively, are operated in the auxam, R845,

/ the link are.

and the winding iliary or common equipment. The relay R858 operates the gang relay R2B0and the relays R885, R850 and R858 operate the unit relays R200, R205, R2l0, R2I5 and R220, respectively, in the finder switch 200, to connect the lines 8|, 8;, 88, 81 and 88, respectively, to

Operation of the finder switch to extend a call initiated at a telephone station connected to an even-numbered line to an idle lim t A call is initiated at a telephone station connected to an even-numbered line by removing the ,receiver of the telephone instrument from its associated switch hook, thereby completing a circuit between the telephone station and the line relay individual to the even-numbered line. For example, when a call is initiated at the telephone station IB connected to the line 20, the line relay RI25, individual to the line 20, is operated, the operating circuit of the line relay R|25 extending from ground at RI25 by way of the upper winding of R|25, RAIZI, the conductor C|208 of the line 20, the telephone instrument at the telephone station IB, the conductor C|208 of the line 20, RA|22 and the lower winding of RI28 to battery. Upon operating, the line relay RIZI completes at RAI21 an operating circuit for the relay R800 in the common equipment, this circuit extending from ground at RA|21 by way of RAIN, CI2I2, the winding of R800, RA809, RA882, RA821, etc., RA8I1, RA801 and the resistor 888 to battery. The line relay R|25 also prepares at RA|28 a circuit for serially energizing the relays R880 and R85 ment. 1

in the common equip CI235, RA242, CI22I and the a point in the series operating circuit of I l9 Upon operating. the relay R000 completes at RA000 an obvious holding circuit for itself, and

' completes at RAOI the series operating circuit of operates and prepares at RA03I a circuit for ene gizing the group unit or subgroup relay R220 in the finder switch 200, and connects its relatlvely low resistance lower winding in parallel with its upper winding to cause the relay R000 to be operated in series with the relay R000.

Upon operating, the relay R055 completes at RA050 an obvious holding circuit for itself, completes at RA051 a circuit for energizing the control relays R230 and R240 in parallel and prepares at RA050 a circuit for energizing the'unit relay R220 in the finder switch 200. The operating circuit of the relays R230 and R240 extends trom ground at R A051 by way or Cl241, RA202, CHM and the winding of R230 and R240 in parallel to battery.

Upon operating, the relay R240 completes at RA242 the operating circuit of the gang relay R210, completes at RA250 the operating circuit of the group unit relay R225, and completes at RA240 the operating circuit of the unit relay R220; the operating circuit of the gang relay R210 extending from ground at RA000 by way of winding of R210 to battery: the operating circuit of the group unit relay R220 extending from ground at RAO0I by way of arm, aazso, CI255 and the winding of R225 to battery; and the operating circuit or the unit relay R220 extending from ground at RA050 by way of CI343, RAMS, (H254 and the winding of R220 to battery. The relay R240 also completes at RA25I a circuit for energizing R000, this circuit extending from ground at R000, by way of the-winding of R000, C|245, RA25I, Cl250, the

'link conductor Cl203 of the link 300, RA355,

RA335, and the upper winding of the line relay R3I0 to battery. Upon operating, the relayR 600 interrupts at RA002 a point in the operating circuits of R600, ROI0, etc., and interrupts-at RAGGI R030 and one of the relays R035, R040, etc.', thereby to busy the allotter 000 to other calls. I

The gang .relay R210 operates to close its contact springs .to connect the lines between 20 and 20 through to the armature springs of the unit relays; the group unit relay R225 operates to disconnect its aunaturesRA220, RA221, RA220, RA229, from the conductor CI250, CI255, CI251, CI259, respectively, and to connect these armatures to the conductors Cl254, CI250, CI200 and Cl200, respectively; and the unit relay R220 operates to connect the line 20 to the link circuit 01 the link 300. When the line 20 is connected. through to the link circuit, the line relay R3I0 'is operated, this circuit extending from ground at RA4I2 by way of the link conductor CI202, RA052, the link conductorCl20I, RA220, CI254, RA222', the contact springs of the gang relay R210, the conductor CI202 of the line 20, the

them

basis telephone instrument at the telephone station IB, the conductor (H200 or the line 20, the contact springs of the gang relay R210, RA220',

CI250, RA221, the link conductor CI200, RAlII,

5 M000 and the upper winding of R0 II to battery.

Upw aerating, the line relay R0l0 completes at R0 a the above-traced circuit for operating the link impulsing relay R000, interrupts at RA2I2 a point in the priming circuit for RIM, and prepares at RAOI2 a point in the path for applying ground to the control conductor 'Cl204.

Upon operating, the link impulsing relay R205 completes at RAIN! an obvious circuit for energizing the hold relay R020 and forapplying ground to the control conductor C l 204, thereby to mark the link 300 as busy in the allotter and to mark the calling line as busy. When the control conductor CI204 is ground, the look-out relay RI l5 and the cut-oil relay RI 20, individual to the line 20, are operated, the circuit for energiing these relay extending from the grounded control conductor CI204 by way of RA220, CI250, RA224', the contact springs of the gang relay R210, the control conductor CI205 of the line 20, the winding oi R| and the winding of RI I5 to battery. Upon operating, the cut-off relay RI20 interrupts at RAI 2i and RAI22 the operating circuit oi the line relay RI25. The line relay RI25 then restores and interrupts at RAI21 the holding a circuit or the relay R000 and interrupts at- RAI20 th series holding circuit of the relays R000 and R055, causing the latter relays to restore. The lock-out relay RII5 operates and interrupts at -RAI l1 a turther point in the holding circuit of the relay R000 and interrupts at RAI III a further point in the series'holding circuit of the relays R030 and R055.

Upon operating, the hold relay R320 completes at RA322 a holding circuit for itself, completes at RA323 a path for applying multiple ground to the control conductor CI204 in order to retain the cut-oil relay RI20 and the lock-out relay RI l5, individual to the line 20, operated during impulsing periods, and completes at RA32I holding circults for the operated gang relay R210, the operated group unit relay R225 and the operated unit relay R220,in the finder switch 200. The holding circuit of the operated gang relay R210 extends from ground at RA304 by way of RA32I, CI25I, the contact springs of R210 and the winding of R210 to battery. The holding circuit of the operated group unit relay R225 extends from the grounded conductor CI25I by way of RA220 and the winding of R225 to battery, while the holding circuit of the'operated unit relay R220 extends from the grounded conductor CI25I by way of RA22I and the winding of R220 to battery. The hold relay R320 also completes at RA225 a circuit for energizing the start relay, not shown, so of the dial and busy tone apparatus 040, thereby to initiate the operation oi! this" apparatus to return dial tone to the telephone instrument at the telephone station IB as reviously explained. The party initiating the call at the telephone "(station IB upon receiving dial tone is informed that a link has been seized and that he may operate the .dialing mechanism associated with the telephone instrument to extend the call from the link to the called line."

7o In a similar manner, when calls are initiated erated in the common equipment. The relay 

